Ligand-gated ion channels (LGICs), also referred to as ionotropic receptors or channel-linked receptors, are a group of transmembraneion channels that are opened or closed in response to the binding of a chemical messenger (i.e., a ligand),[1] such as a neurotransmitter.[2]

The prototypic ligand-gated ion channel is the nicotinic acetylcholine receptor. It consists of a pentamer of protein subunits, with two binding sites for acetylcholine, which, when bound, alter the receptor's configuration and cause an internal pore to open. This pore allows Na+ ions to flow down their electrochemical gradient into the cell. With a sufficient number of channels opening at once, the intracellular Na+ concentration rises to the point at which the positive charge within the cell is enough to depolarize the membrane, and an action potential is initiated.

The cys-loop receptors contain a characteristic loop formed by a disulfide bond between two cysteine residues and are subdivided into the type of ion that the corresponding channel conducts (anionic or cationic) and further into families defined by the endogenous ligand. They are usually pentameric.

Ligand-gated ion channels are likely to be the major site at which anaesthetic agents and ethanol have their effects, although unequivocal evidence of this is yet to be established.[7][8] In particular, the GABA and NMDA receptors are affected by anaesthetic agents at concentrations similar to those used in clinical anaesthesia.[9]